/* InputBuffer.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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along with GNU Classpath; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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package gnu.javax.crypto.sasl;

import gnu.java.security.Registry;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.math.BigInteger;

/**
 * The implementation of an incoming SASL buffer.
 * <p>
 * The data elements this class caters for are described in [1].
 * <p>
 * References:
 * <ol>
 * <li><a
 * href="http://www.ietf.org/internet-drafts/draft-burdis-cat-srp-sasl-09.txt">
 * Secure Remote Password Authentication Mechanism</a>;<br/>
 * draft-burdis-cat-srp-sasl-09,<br/> <a
 * href="mailto:keith@rucus.ru.ac.za">Keith Burdis</a> and <a
 * href="mailto:raif@forge.com.au">Ra&iuml;f S. Naffah</a>.</li>
 * </ol>
 */
public class InputBuffer
{
  /** The internal buffer stream containing the buffer's contents. */
  protected ByteArrayInputStream in;
  /** The length of the buffer, according to its header. */
  protected int length;

  /**
   * Constructs a SASL buffer given the buffer's encoded form, including its
   * header bytes.
   * 
   * @param frame the encoded form, including the header bytes, of a SASL
   *          buffer.
   * @throws SaslEncodingException if the buffer is malformed.
   */
  public InputBuffer(byte[] frame) throws SaslEncodingException
  {
    this();

    if (frame.length < 4)
      throw new SaslEncodingException("SASL buffer header too short");
    length = (frame[0] & 0xFF) << 24
           | (frame[1] & 0xFF) << 16
           | (frame[2] & 0xFF) << 8
           | (frame[3] & 0xFF);
    if (length > Registry.SASL_BUFFER_MAX_LIMIT || length < 0)
      throw new SaslEncodingException("SASL buffer size limit exceeded");
    in = new ByteArrayInputStream(frame, 4, length);
  }

  /** Trivial private constructor for use by the class method. */
  private InputBuffer()
  {
    super();
  }

  /**
   * Returns an instance of a SASL buffer given the buffer's encoded contents,
   * excluding the buffer's header bytes.
   * <p>
   * Calls the method with the same name and three arguments as:
   * <code>getInstance(raw, 0, raw.length)</code>.
   * 
   * @param raw the encoded form, excluding the header bytes, of a SASL buffer.
   * @return a new instance of {@link InputBuffer}.
   */
  public static InputBuffer getInstance(byte[] raw)
  {
    return getInstance(raw, 0, raw.length);
  }

  /**
   * Returns an instance of a SASL buffer given the buffer's encoded contents,
   * excluding the buffer's header bytes.
   * 
   * @param raw the encoded form, excluding the header bytes, of a SASL buffer.
   * @param offset offset where to start using raw bytes from.
   * @param len number of bytes to use.
   * @return a new instance of {@link InputBuffer}.
   */
  public static InputBuffer getInstance(byte[] raw, int offset, int len)
  {
    InputBuffer result = new InputBuffer();
    result.in = new ByteArrayInputStream(raw, offset, len);
    return result;
  }

  /**
   * Converts two octets into the number that they represent.
   * 
   * @param b the two octets.
   * @return the length.
   */
  public static int twoBytesToLength(byte[] b) throws SaslEncodingException
  {
    final int result = (b[0] & 0xFF) << 8 | (b[1] & 0xFF);
    if (result > Registry.SASL_TWO_BYTE_MAX_LIMIT)
      throw new SaslEncodingException("SASL MPI/Text size limit exceeded");
    return result;
  }

  public boolean hasMoreElements()
  {
    return (in.available() > 0);
  }

  /**
   * Decodes a SASL scalar quantity, <code>count</code>-octet long, from the
   * current buffer.
   * 
   * @param count the number of octets of this scalar quantity.
   * @return a native representation of a SASL scalar (unsigned integer)
   *         quantity.
   * @throws SaslEncodingException if an encoding exception occurs during the
   *           operation.
   * @throws IOException if any other I/O exception occurs during the operation.
   */
  public long getScalar(int count) throws IOException
  {
    if (count < 0 || count > 4)
      throw new SaslEncodingException("Invalid SASL scalar octet count: "
                                      + String.valueOf(count));
    if (! hasMoreElements())
      throw new SaslEncodingException("Not enough bytes for a scalar in buffer");
    if (in.available() < count)
      throw new SaslEncodingException("Illegal SASL scalar encoding");
    byte[] element = new byte[count];
    in.read(element);
    long result = 0L;
    for (int i = 0; i < count; i++)
      {
        result <<= 8;
        result |= element[i] & 0xFFL;
      }
    return result;
  }

  /**
   * Decodes a SASL OS from the current buffer.
   * 
   * @return a native representation of a SASL OS.
   * @throws SaslEncodingException if an encoding exception occurs during the
   *           operation.
   * @throws IOException if any other I/O exception occurs during the operation.
   */
  public byte[] getOS() throws IOException
  {
    if (! hasMoreElements())
      throw new SaslEncodingException(
          "Not enough bytes for an octet-sequence in buffer");
    final int elementLength = in.read();
    if (elementLength > Registry.SASL_ONE_BYTE_MAX_LIMIT)
      throw new SaslEncodingException("SASL octet-sequence size limit exceeded");
    if (in.available() < elementLength)
      throw new SaslEncodingException("Illegal SASL octet-sequence encoding");
    byte[] result = new byte[elementLength];
    in.read(result);
    return result;
  }

  /**
   * Decodes a SASL EOS from the current buffer.
   * 
   * @return a native representation of a SASL EOS.
   * @throws SaslEncodingException if an encoding exception occurs during the
   *           operation.
   * @throws IOException if any other I/O exception occurs during the operation.
   */
  public byte[] getEOS() throws IOException
  {
    if (in.available() < 2)
      throw new SaslEncodingException(
          "Not enough bytes for an extended octet-sequence in buffer");
    byte[] elementLengthBytes = new byte[2];
    in.read(elementLengthBytes);
    final int elementLength = twoBytesToLength(elementLengthBytes);
    if (in.available() < elementLength)
      throw new SaslEncodingException(
          "Illegal SASL extended octet-sequence encoding");
    byte[] result = new byte[elementLength];
    in.read(result);
    return result;
  }

  /**
   * Decodes a SASL MPI from the current buffer.
   * 
   * @return a native representation of a SASL MPI.
   * @throws SaslEncodingException if an encoding exception occurs during the
   *           operation.
   * @throws IOException if any other I/O exception occurs during the operation.
   */
  public BigInteger getMPI() throws IOException
  {
    if (in.available() < 2)
      throw new SaslEncodingException("Not enough bytes for an MPI in buffer");
    byte[] elementLengthBytes = new byte[2];
    in.read(elementLengthBytes);
    final int elementLength = twoBytesToLength(elementLengthBytes);
    if (in.available() < elementLength)
      throw new SaslEncodingException(
          "Illegal SASL multi-precision integer encoding");
    byte[] element = new byte[elementLength];
    in.read(element);
    return new BigInteger(1, element);
  }

  /**
   * Decodes a SASL Text from the current buffer.
   * 
   * @return a native representation of a SASL Text.
   * @throws SaslEncodingException if an encoding exception occurs during the
   *           operation.
   * @throws SaslEncodingException if the UTF-8 character encoding is not
   *           supported on this platform.
   * @throws IOException if any other I/O exception occurs during the operation.
   */
  public String getText() throws IOException
  {
    if (in.available() < 2)
      throw new SaslEncodingException("Not enough bytes for a text in buffer");
    byte[] elementLengthBytes = new byte[2];
    in.read(elementLengthBytes);
    final int elementLength = twoBytesToLength(elementLengthBytes);
    if (in.available() < elementLength)
      throw new SaslEncodingException("Illegal SASL text encoding");
    byte[] element = new byte[elementLength];
    in.read(element);
    return new String(element, "UTF8");
  }
}